The brain's response to nicotine introduction

For centuries, people have chewed and smoked tobacco, which comes from the
plant nicotiana tabacum. The reason tobacco is used by so many people is because
it contains a powerful drug known as nicotine.

When tobacco is smoked, nicotine is absorbed by the lungs and quickly moved
into the bloodstream, where it is circulated throughout the brain. All of this
happens very rapidly. In fact, nicotine reaches the brain within 8 seconds after
someone inhales tobacco smoke.
Nicotine can also enter the bloodstream through
the mucous membranes that line the mouth (if tobacco is chewed) or nose (if
snuff is used), and even through the skin.

Nicotine affects the entire body. Nicotine acts directly on the heart to
change heart rate and blood pressure. It also acts on the nerves that control
respiration to change breathing patterns. In high concentrations, nicotine is
deadly, in fact one drop of purified nicotine on the tongue will kill a person.
It's so lethal that it has been used as a pesticide for centuries.